Conventionally, a technique relating to a light reception power monitor of an optical module has been developed and disclosed in various pieces of literature. Patent Literature 1 discloses a light power meter for correcting light reception sensitivity using a correction coefficient in order to precisely measure light power of measured light even when light reception sensitivity of a light receiving element deteriorates over time. Patent literature 2 discloses an optical LAN system adapted to control a light output signal of an optical reception/transmission module on the basis of a value of a light reception power monitor. Patent literature 3 discloses a light reception power monitor circuit that has improved precision by correcting offset caused by dark current or leak current of an electric circuit. Patent Literature 4 discloses a technique for compensating for a difference and uncertainty in data age between a plurality of measurements by an electron avalanche photodiode (APD) in measuring changes in position, length, distance, or optical length using an interferometer.
The SFF Committee (Small Form Factor Committee) has created SFF-8472 specification for diagnostic monitoring interface for optical transceivers (see Non-Patent Literature 1). When a measured value of a light reception power monitor in an optical module is corrected by the specification, an MPU (Microprocessing Unit) inputs the measured value in a calculation formula for linear interpolation, fourth-order curve interpolation, or the like, to calculate a correction value. In the SFF-8472 specification, on the basis of a measured value of a light reception power monitor, a calculation formula for a fourth-order interpolation is executed to calculate an actual value (hereinafter referred to as correction value) of light reception power.Actual value=A×ADC value4+B×ADC value3+C×ADC value2+D×ADC value+E 
In the above calculation formula, “ADC value” represents a measured value obtained by converting an analog value obtained by converting received light into an electric signal using a photodiode into a digital value by an A/D converter. In addition, A, B, C, D, and E represent constant values for correction.
In general, in order to achieve miniaturization, low power consumption, and low cost in an optical module, installation of an inexpensive and low-speed MPU is desirable. However, the use of such an MPU makes it difficult to calculate an actual value on the basis of a measured value of a light reception power monitor by executing high load processing such as a fourth-order interpolation in a short time.
When correcting a measured value of the light reception power monitor by the inexpensive and low-speed MPU without any fourth-order interpolation calculation, an actual value corresponding to the measured value can be acquired by causing the MPU to create in advance a table storing a relationship between measured value and actual value and to refer to the table.
Patent Literature 3 and Patent literature 4 describe the above conventional techniques. Patent Literature 3 discloses a structural example of a light reception power monitor, and Patent Literature 4 discloses a technique for referring to a lookup table to compensate for APD characteristics.